The invention relates to a vacuum pressure measuring device with an electron source and with a reaction zone for the formation of ions through impact ionization.
The invention relates, in particular, to vacuum pressure measuring engineering or to vacuum pressure measuring devices based on the ionization of gas molecules for the measurement of total pressure (ionization manometer) as well as also for the measurement of partial pressure (mass spectrometer).
For the ionization of the gas molecules in a vacuum pressure measuring device for the measurement of total pressure (ionization manometer) as well as also for the measurement of partial pressure (mass spectrometer) an electron source is necessary, located in the immediate proximity to the ionization volume as is known in prior art. Under measuring conditions in vacuum pressure ranges from less than 1 Pa (10−2 mbar), and with high pressure measuring tubes 1 to 2 decades higher, the electron source has the task of emitting electrons into the ionization volume. For the electron emission primarily hot cathodes (thermionic emission) have so far been utilized. Electron sources with field emitters (field emission) furthermore have also been proposed for vacuum pressure measurements, which, with respect to the conditions of application and/or to the production expenditure, have so far not become commercially widely established.
Due to the principle involved, interaction between the electron source and the ionization or measuring volume is necessary in such vacuum pressure measuring cells. Fast venting of the arrangement, for example when opening a process vacuum chamber for loading workpieces to be treated, is especially problematic since the oxygen intrusion leads to the destruction of the active, electron emitting thermionic cathode (cf. incandescent lamp). Special protective measures against this must be taken each time. Further problems are generated in case of contaminations, especially through forepumps contaminated with operating fluid, such as sliding vane rotary pumps. Aggressive process and etching gases frequently utilized today, such as for example silane and gases based on chlorine and fluorine, are also highly problematic. When using very aggressive process gases, it is therefore customary to protect vacuum measuring devices based on ionization, which are necessary for the base pressure measurement, against the process with a valve, such as for example an all-metal vane, which leads to considerable additional costs and makes the application feasibilities difficult and limited.